Method and means for holding diamonds during the polishing operation



UNITED STATES PATENT OFFICE.

CLYDE J'. COLEMAN, OF NEW EROCHELLE, NEW YORK, ASSIGNOR TO STERN-COLEMANDIAMOND MACHINE COMPANY, INC., OF NEW YORK, N. Y.

METHOD AND MEANS FOR HOLDING DIAMONDS DURING THE POLISHING OPERATION.

N 0 Drawing.

ing Diamonds During the Polishing Operation, of which the following is aspecification.

The invention relates to a new process and means for holding diamondsduring the "polishing thereof and the object of the in vention is toprovide a process and means which Wlll hold diamonds during pollshmg byadhesion to the polished faces thereof, as

well as to the natural or unpolished surface.

This application is a continuation in part of my prior application,Serial No. 74,076, filed January 25, 1916, and Serial No. 34,161, filedJune 15, 1915, and a continuation in part of my prior applications,Serial No. 808,280, filed December 22, 1913; Serial No.

808,279, filed December 22, 1913; Serial No.

710,622, filed Jul 20, 1912, and Serial No. 710,621, filed Ju y 20,1912, the invention being claimed broadly herein, and more specificallyin said prior applicatiops.

In the polishing of diamonds, it has been the practice to hold smalldiamonds and until recently large stones also in the polishin tool bypartially embedding it in a body 0 metal in a semi-molten state,contained in.

a small brass basin or dop, the diamond being held in position by themetal after the metal has cooled. This method suffers from thedisadvantage that it is necessary from time to time to soften the metaland readjust the diamond to expose a different part thereof forpolishing, as it is not possible to expose at one time all parts of thediamond on one side of the girdle line. It is also common practice tolock the larger stones in a clamping device, but this device is verydifficult to adjust so as to hold the diamond at the correct angle, aswell as being subject to the disadvantages noted above. The diflicultyin holding diamonds during the polishing operation, as distinguishedfrom other precious stones, is due to the extreme hardness of thediamond, which necessitates applying great pressure, with resultantgreat friction and generation of great heat. Diamond polishing isparticularly a difficult operation and unlike any other lapi-Specification of Letters Patent.

Application filed November 20, 1916.

Patented Jan. 4, 1921.

Serial No. 132,277.

dary work, because with all other gems there is something harder thanthey are, which will easily abrade them and not require any specialspeed or pressure to polish them, but the diamond being the hardestknown substance, it must be polished with its own dust. This requiresgreat lap speed, great pressure and also a precise grain presentation tothe direction of movement of the lap, with the result that a hightemperature is generated and often an almost in stantaneous rise fromlow red heat to white red heat is developed when a hard spot isencountered and then dropping back suddenly to the normal red heat.

The polishing of the diamond is, therefore, a radically differentproposition from the polishing of other stones or semiprecious gems,with the latter so little heat is generated and so little pressurerequired, that ordinary silicious or wax adhesives may be used. Certaincements have been used to hold diamonds during the roughing out orbruting operation, but in such cases, the cement holds the diamond byanchorage or mechanical interlocking with the irregularities in thesurface of the diamond, and not by adhesion to the surface, and hencesuch cements are useless for holding diamonds during the final orpolishing stages, because they have not sufiicient adherence to thepolished faces.

I have discovered, however, that if an adhesive be compounded whichcontains suflicient of an oleaginous" constituent and matter giving it acertain relative malleability and being sufficiently refractory, such anadhesive will adhere satisfactorily to the polished surfaces of thediamond so as to hold the diamond rigidly against the strains of thepolishing operation with the cement applied only to the polished facesof the diamond on one side of the girdle.

nized as oily) of wetting the polisheddim mond surface. Water is sald-to he non Wetting with respect to such a surface, diamonds show greatadherence to greasy surfaces, and by using an oleaginous or unctuousconstituent in the adhesive, the adhesive will adhere strongly to thepolished diamond surface, and I believe this is due to the fact thatoleaginous or unctuous material will readily flow or spread out on sucha surface, adhering to substantially all parts thereof, while with othercements the material actually touches the polished surface at few if anypoints, there being a thin space or layer of air between the cement anddiamond surface, due to the non-wetting character of the cement uponsuch surface, which prevents any substantial adhesion taking place. Thediamond being carbon, differs radically from other gems in this respect.Non-wetting ornon-oleaginous cements, suitable for other gems, andso-called diamond cutters cement, can therefore only hold diamonds bymechanical action or anchorage, rather than by real adhesion.

The cement or adhesive in use must, however, also possess eithersubstantially the same coeflicient of expansion as the diamond, or elsea certain malleability, such, that under the great and sudden changes intemperature, causing relative expansion and contraction between it andthe diamond, the cement will not be disrupted, disintegrated, dislodged,or otherwise loosened from the diamond surface. Other gems have aconsiderable coefficient of expansion, like that of ordinary cements.But the coefficient of expansion of the diamond is found to beextraordinarily small. Hence, if the adhesive and diamond durin theolishing operation do not have su stantially the same coeflicient ofexpansion, the adhesive expands and breaks away from-the diamond. I havefound that an adhesive may be made which is capable of sufficientyielding to mechanical deformation under pressure or slight shockwithout too much mechanical weakening, to prevent its holding the diamond rigidly by attachment to the polished faces thereof. This does notnecessarily mean elasticity, which implies a return to the originalform, nor does plastic precisely express the meaning, because itsignifies absence of elasticity, which is not necessarily absent. Thebest term to express this property of which I am aware is malleability,in the sense that in s ite of a certain elasticity, there is not sucient rigidity to prevent its yielding to excessive straimwithoutbreakage, and I use the term malleable with this meaning herein. Thismalleability maybe inherent in a single ingredient or may be produced bydiscontinuity of physical make up, which I may call structuralmalleability, the first being illustrated by certain colloids, and thesecond by certain plasters, as'well ,aa by'oneof the examples but.of mycement made up of flakes of material like graphite, bound together atsome points, but capable of relative movement or adjustment withoutdisintegration or breaking up of the mass. Such an adhesive will havethe requisite malleability to yield in either direction to such anextent that stresses of unequal expansion or contraction by heat arecompensated for by yielding without breakage of the joint.

Accordingly, in carrying out my invention I choose a substance oringredients which will not only during the polishing operation besufliciently refractory and rigid, but also will have the requisitemalleability and contain sufiicient oleagino g matter to give goodadherence to the diamond surfaces. The material is preferably oleaginousabout 300, F but I find that the adhesive may be composed largelyofmatter not oleaginous, as all the matter in the cement need not beoleaginous to give good results. The adhesive is preferably mixed up inthe form of a paste and then baked on to the diamond. It is preferablycomosed chiefly of matter refractory at 700 so that it will be infusibleat 600 F.

One method of compounding such an adhesive is as follows: Take 50 partsby bulk of Dixons stove polish (composed of 60% clay and 40% graphite),selecting that which is dense, hard and of good body and not friable,crumbly, sooty or of a dirty nature, and 50 parts by bulk of pure Whitesoapstone clay, such as the talcum or steatite varieties, and 20 partsby bulk of borax or boric acid, and 10 parts by bulk of nitrate of lead,and with these in finely divided condition, mix them thoroughly. Nitrateof antimony is then prepared in the form of a concentrated solution, byallowing strong nitric acid to act on an excess of antimony for aboutten to sixteen hours. The powdered mixture is then made into a thick,creamy paste with a sufficient amount of the nitrate of antimonysolution. This paste is allowed to stand for 24 hours or longer and thenit is made again into a similar paste with water.

Better results have been obtained by omitting the nitrate of lead andusing the antimony alone with the clay, graphite and borax. Thus 32,parts by weight of the Dixons stove polish, 16 parts by weight of clay,and 12 parts by weight of borax may be mixed with the antimony solutionas above described, except that it is preferable to dilute the antimonysolution with an equal amount of water before using it to make thepaste.

In either case a convenient way of mixing the dry raw materials is torind them together. What I have calle antimony nitrate I prefer to makeby breaking the metallic antimony of good quality up into lumps aboutthe size of a pea (i. 6.; about 35 mm.) and to place 1 oz. of theselumps in an open vessel about 1 in diameter and add 4 fluid ounces ofconcentrated G. l. nitric acid. This I allow to stand open, or onlyloosely covered over night, preferably about 16 hours in a warm place(about 75 F. to 80 F.) whereupon the liquor takes on a greenish colorand the bottom is covered between the antimony lumps with whitishpowder. In the morning I add four fluid ounces of water, shakethoroughly, allow to settle and decant the clear liquid through a filterinto a stock bottle from which portions can be taken fromtime to timefor use. This product I have called antimony nitrate but chemists tellme it is really a solution of antimonic acid further acidified with someunconsumed nitric acid. When in either case this antimony solution isused to make a paste with the dry ground Dixons stove polish, clay, etc,I prefer to make the paste of the consistency obtained by taking 134grains of dry powder and grinding into it 34 drops of the antimonyliquid on a ground glass plate with a glass pestle, just as colors areground together or with oils for china painting, until the paste is of asmooth even consistency. This paste I then spread thin on a glass plateand allow to thoroughly dry for 24 hours in a warm room. And then breakup the mass and regrind 72 grains. of it in the same way with 6 drops ofsaturated boracic acid solution and use it while still moist.

Obviously other materials than those mentioned may be used to mix withthe clay to bring out its adhesive qualities, hence the invention is notlimited to the precise materials and quantities named.

The paste is placed between the diamond and the arbor, preferably beingapplied in considerable body, so that it will be anchored in the arborand will form a stem within the arbor for adhesively holding thediamond, and it is baked with the parts held together, at a hightemperature, preferably in a non-oxidizing environment, as by inclosurein a retort containing carbon monoxid or nitrogen gas. The heat is firstapplied at a low temperature to dry the material and is graduallyincreased to 800 F. or higher. The temperature required will vary,however, depending upon the particular ingredients used and theirproportions.

. The baking usually requires from 25 to 30 minutes. The cement ispreferably gradually cooled.

Another formula which has given fair results contains a base consistingof a material known as Dixons stove polish, this material beingapparently composed of clay and graphite. and I have at times replacedthis stove polish by a mixture of clay and graphite, about 60% of clayand 40% of graphite, this base being compounded with the followingmaterials in the following proportions by volume: base, 100 parts;nitrate of lead, 10 parts; nitrate of antimony 15 parts; boracic acid,20 parts.

Other formulae which have been used with more or less success are:

(1) Carbid of iron 13 parts; borax 2 parts; tungstic oxid 3 parts; andsufficient water to make the composition into a thick paste.

(2) Powdered silica (commercially known as quartz) combined with boracicacid and phosphatic or zinc oxid cements, or a combination of calciumoxid and borax, or other constituents containing suflicient oleaginousmatter.

parts finely powdered anthracite coal; 25 parts finely powdered gumshellac; 50 parts boracic acid; 25 parts chlorid of magnesium or chloridof calcium, and a sufficient solution of caramelized cane sugar to makethe whole into a stiff paste. Instead Sulfids of metals, or metalsandsulfur may also be sometimes used. But in each case, however, one ormore of the ingredients should either be oleaginous or contain, eitherinherently or as impurity, suflicient oleaginous, or diamond wetting,matter to bring about the desired adhesion to the diamond surface.

While I have described in detail certain formulae for an adhesive whichmay be used for securing the diamonds for polishing, it will beunderstood that other formulae, having different ingredients, but havingthe characteristics mentioned may well be used. as well as otheradhesives containing the same materials, but in different quantities.Accordingly, my invention in its broader aspects is not limited to thedetails described.

What I claim as new and desire to secure by Letters Patent is:

1. The method of polishing diamonds peratures of the polishing operationand having oleaginous properties so as to wet all parts of the surfaceof the diamond brought into contact with the cement and cause adhesionof the cement to the diamond over all parts of such contacting surface,causing the cement to set, supporting the cement, and polishing thediamond on the opposite side of the girdle.

2. The method of supporting diamonds for the polishing operation whichconsist in embedding a diamond on one side only of its girdle in asupporting cement adapted to Withstand the high temperatures of thepolishing operation and having oleaginous properties so as to Wet allparts of the surface of the diamond brought into contact with the cementand cause adhesion of the cement to the diamond over all parts of suchcontacting surface, causing the cement to set, and supporting thecement.

3. A setting for holding diamonds during the polishing operationcomprising a support, a cement, securely held by the support, adapted toWithstand the high temperatures of the polishing operation and havingoleaginous properties so as to Wet every part of a diamond surfaceembedded in it, and a diamond embedded in said cement on one side onlyof its girdle and adhering thereto throughout all parts of its entireembedded surface so as to Withstand the strains, heat and pressure ofthe polishing operation.

4. A setting for diamonds during the polishing operation comprising asupport, a cement, securely held by the support, adapted to withstandthe high temperatures of the polishing operation and having oleaginousproperties so as to Wet every part of a diamond surface embedded in itand having malleable properties adapted to preserve the continuity ofadhesion between the diamond and the cement during the expansions andcontractions produced in the polishing operation, and a diamond embeddedin cement on one side only of its girdle, and adhering theretothroughout all parts of its entire embedded surface so as to Withstandthe strains, heat and pressure of the polishing operation.

In testimony whereof, I have signed my name to this specification.

CLYDE J. COLEMAN.-

